July 29, 1875] 



NATURE 



255 



railing, and the lead by which the iron is fastened 

 into the stone, and rain or atmospheric moisture, as the 

 liquid or exciting medium. The wasting away of the iron 

 just above the coping stone is the result of the galvanic 

 action set up between the two metals (iron and lead) 

 and the liquid (the moisture of the atmosphere). To 

 preserve an iron railing therefore it becomes necessary to 

 dispense with the presence of lead ; nothing can be better 



than the adoption of an iron coping in place of stone. 

 As knowledge spreads, so practical results follow, and 

 many modern examples of iron railings will be found to 

 fulfil the conditions above indicated as necessary to ensure 

 a "long life" 



All connoisseurs of malt and hop beverages agree that 

 ale drinks much sharper and is more tasty to the palate out 

 of a pewter tankard than out of a glass. At a refreshment 



Fig. 4t.— Voltiic Batlery.connected,in series, in illustration] Jof tl 



nal resiiiatue of the battery. 



bar the demand is more often for " half a pint of bitter " 

 (served in a metal vessel) than for a " glass of bitter ;" and 

 common belief in this instance is correct. Here we have 

 a galvanic current set up by two liquids and one metal ; 

 the effect of the electric current so generated being to 

 sharpen and improve the taste of the beverage to' the 

 palate by reason of electric action. In this example there 

 are the two liquids— the beverage, and the saliva of the 

 mouth — and one metal — that of the tankard— the resultant 

 effect on the palate of the consumer being an increased 



Fig. 4«.— The Daniell Battery. 



life or vigour in the taste of the beverage. Thus, even in 

 the trivialities of everyday life, electricity has a part to 

 play. The generation of the voltaic current for tele- 

 graphic purposes is based upon one or other of these 

 principles ; and it is essential in telegraphy that the 

 power of the current derived from the battery should 

 be adjusted to the circuit. 

 The strength of the current depends on the electro- 



motive force of the battery and upon the rcsislaticc of the 

 circuit. The precise meaning to be attached to these 

 terms was first pointed out by Ohm in 1827, who showed 

 that the strength of the current is directly proportional to 

 the former and inversely proportional to the latter. The 

 statement of this relation is commonly spoken of as 

 "Ohm's Law." The total resistance of a telegraphic 

 circuit is made up partly of the resistance of the battery, 

 and its necessary connections, and partly of the resistance 

 of the metallic conductor constituting the litie. Conse- 



quently the law established l>y Ohm may be expressed as 

 follows : — 



Thejavailable effective force of any cunent = the electromotive 

 •..V force of the Battery— (the resistance of the Battery + the 

 {^^ V. resistance of the line wire).jj^ 



It has been found [that in any given case the electro- 

 motive force and resistance depend upon conditions that 

 may be thus stated :— 



